Download A hands-on approach for learning the dynamics of antibiotic resistance

Why Finish Your Antibiotics?
A hands-on approach for learning the dynamics of antibiotic resistance
Background Information
Antibiotic drug therapy is the cornerstone of society’s warfare against infectious disease. However, resistance to these drugs is rapidly
emerging as major threat to public health. The capacity of bacteria for mutation, exchange of genetic material and rapid reproduction
can result in selection for more resistance stains. Antibiotics are often inappropriately prescribed for non-bacterial infections, such as
the flu and common cold, which increases the opportunities for bacterial resistance. Sobering studies from the Centers of Disease
Control and Prevention have shown that 25 to 50 percent of all outpatient prescriptions are inappropriate.
Another common medical misuse of antibiotics is the patient how shorten the course of treatment when his/her symptoms subside, or
skip days of the antibiotic regime, altering the bacterial response and potentially triggering a re-infection.
In addition to their medical applications, antibiotics are used as pesticides on fruit trees and fed to livestock to prevent disease and
promote growth. This is legal, but controversial in the U.S. and has been banned in Europe. Recent students suggest that the
cultivation of resistant bacteria may pose a threat to human health as well (van den Bogaard et al., 2000, 2001; et al., 2002).
Materials & Methods
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Divide class into eight groups. Each group will investigate four strains of bacteria.
Each group needs four different types of bean to represent bacteria. Each group starts with:
- 40 pieces of strain 1 Least Resistant
- 30 pieces of strain 2
- 20 pieces of strain 3
- 10 pieces of strain 4 Most Resistant
For ease, keep each strain in a different cup (but, in reality the strains would be intermingling within the infected person’s
body).
Set of Assumptions
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Each type of bean represents a strain of infectious bacteria. Imagine that the bacterium is a pathogen that is currently
presenting antibiotic resistance problems such as Neisseria gonorhoeae, Mycobacterium tuberculosis, or Staphylococcus
aureus.
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The strains vary in their level of antibiotic resistance. Strain 1 is very susceptible to antibiotics. Strain 4 is most resistant to
antibiotics. The relative resistance of a strain reflected in the number of days of treatment necessary before the antibiotic
begins destroying that strain. For example, strain 1 is susceptible to the antibiotic on the first day of the treatment while strain
4 is not affected until the fourth day of the treatment. Strains 2 and 3 become susceptible on the second and third days of
treatment, respectively.
At the beginning of each “day”:
1.
2.
3.
4.
The antibiotic is taken (except when skipped or treatment ended early)
Each day, 10% of the TOTAL numbers of bacteria (from all four strains) are removed through the action of the specific and
non-specific mechanisms of the host immune system. Strains are assumed to be equally susceptible to these immune
responses. The total number of bacteria to be removed is calculated, and then taken RANDOMLY FROM AMONG THE
FOUR STRAINS. To do this, have a student close his/her eyes and randomly touch on of the four cups holding the bacteria,
them remove a piece from the cup and repeat until the total number to be removed have been taken from the cups. 10% of the
bacteria are removed on day 0 and on each subsequence day.
If the strain is susceptible on that day, then half of those bacteria are removed. For instance, on day 1 of the experiment,
strain 1 would be susceptible and the number of bacteria in those cups would be halved. On day 3 of the experiment, strains
1, 2 and 3 would be susceptible and the number of bacteria in each of those cups would be halved.
If the strain is not susceptible on a certain day, then the number of bacteria is doubled. For instance, on day 1 of the
experiment, strains 2, 3 and 4 would not be susceptible and the number in these cups would be doubled. On day 3 of the
experiment, only strain 4 would not be susceptible and the number of bacteria in this cup would be doubled.
5.
6.
7.
If a day of treatment is missed each of the strains will double and the following day only the least resistant strain will
be susceptible.
After the 4th consecutive day of treatment each of the strains are now susceptible
Each group enters the numbers of each strain present on each day until 0 of the bacteria are counted in each strain or until day
12 of the experiment, whichever comes first. The number of days necessary to each 0 will vary according to the antibiotic
regime.
Each group will investigate a different antibiotic regimen:
Group 1 follows doctor’s orders and the instructions presented above.
Groups 2-5 skip a day of treatment. All strains double on the day treatment is skipped and the “susceptibility clock” is reset
to zero. That is, after missing a day, Strain 1 will be susceptible on the first day the antibiotic treatment is resumed, but it will
take 2 days of treatment before strain 2 is susceptible, three days before stain 3, etc.
● Group 2 skips day 2 of treatment
● Group 3 skips day 3 of treatment
● Group 4 skips day 4 of treatment
● Group 5 skips day 5 of treatment
3. Groups 6-8 discontinue the use of antibiotic before the treatment is complete. By day 5 of treatment, the total number of bacteria
has fallen below the initial population and the “patient” would have begun to feel better. When the antibiotic is not taken, it is summed
that the antibiotics concentration falls rapidly, and therefore all strains will double on that day and each subsequent day.
● Group 6 ends the treatment on day 5.
● Group 7 ends the treatment on day 7.
● Group 8 ends the treatment on day 9.
Data Collection - Group Results
● Each group collects data for the total number of each strain of bacteria on days 1 through 12 of the treatment
regimen they have been assigned. Create a data table for your results
Data Collection - Class Results
● Create a data table to record the total number of bacteria (all 4 strands combined) on days 1 through 12 of all of the treatment
regimens.
● Create a graph (or graphs) that depict the total bacterial count over each day of treatment for each of the eight treatment
regimens.
1.
2.
Group Condition
1
2
3
4
5
6
7
8
Doctor’s
orders
Skip day
2
Skip day
3
Skip day
4
Skip day
5
Ends on
day 5
Ends on
day 7
Ends on
day 9
0
1
Total Bacterial count on each day of treatment(All strains)
2
3
4
5
6
7
8
9
10
11
12
Analysis
1. For your assigned treatment regimen, explain the different dynamics of the more resistant strains as compared to the
very susceptible strains.
2. Compare the effects of the various antibiotic treatment regimens. Which works best at eradicating the infection,
why? Which works least?
3. How does the activity model the process of natural selection in action?